The most successful interrogation of an Al-Qaeda operative by U.S. officials required no sleep deprivation, no slapping or "walling" and no waterboarding. All it took to soften up Abu Jandal, who had been closer to Osama bin Laden than any other terrorist ever captured, was a handful of sugar-free cookies.

Abu Jandal had been in a Yemeni prison for nearly a year when Ali Soufan of the FBI and Robert McFadden of the Naval Criminal Investigative Service arrived to interrogate him in the week after 9/11. Although there was already evidence that al-Qaeda...